The present invention relates to an improved microwave drying apparatus, more particularly to a microwave drying apparatus free from moisture condensation in the apparatus during drying procedure.
As apparatuses for drying materials, various kinds of apparatuses have been designed or developed heretofore. Among them, the microwave drying apparatus is well known. However, if the materials to be treated are dried by using such a microwave drying apparatus, moisture condensation on the inner wall of the drying chamber is caused due to the generation of water vapor evaporated from the materials being dried. As a result, the water drops formed on the inner wall fall down onto the materials and it becomes difficult to obtain materials uniformly dried and the quality of the dried materials is also degraded. Furthermore, the energy of the microwaves is consumed by condensed water, and therefore, the effectiveness of the drying operation is highly reduced.
Although such a problem is encountered even when the drying operation is carried out under the normal pressure condition, it is even more significant when the drying operation is effected at a reduced pressure condition because the drying of the materials is carried out in a completely sealed drying chamber.
In order to prevent the occurrence of moisture condensation, a reduced pressure microwave drying apparatus has been developed and practically used, in which the wall of the drying chamber is heated by a heater. However, in this apparatus, it is innevitable to use microwaves to dry materials and to use a heater to prevent the occurrence of moisture condensation on the inner wall of the drying chamber, that is, it is necessary to use two different heat sources.